The Anthropogenic Global Warming (AGW) Theory

Greenhouse Effect

• The natural phenomenon called the greenhouse effect traps heat in the lower layers of the Earth̵7;s atmosphere. Certain atmospheric gases are transparent to the sun̵7;s visible light but are opaque to infrared radiation given off when sunlight warms the land and oceans. Because the infrared cannot escape into space quickly, the Earth does not suffer the wild temperature swings that happen on the moon, which has no air. Although the effect has kept the Earth hospitable to life, too much trapped heat has led to increased global temperatures and shifts in climate.

Greenhouse Gases

• Scientists use the term "greenhouse gases" to describe those gases that trap heat in the atmosphere, including carbon dioxide, methane and nitrous oxide. Although carbon dioxide, a byproduct of burning fossil fuels, is found in the greatest concentrations of the various greenhouse gases, it traps heat less efficiently than the other gases. Methane is 25 times more potent at blocking infrared light than CO2, and nitrous oxide is nearly 12 times more effective than methane.

Industry and Farming

• Human activities that produce greenhouse gases include large-scale industrial operations and farming. Electric power generation and heating accounted for 41 percent of the 30 billion tons of CO2 produced globally in 2010; the production of steel and iron, concrete and other materials also contributes heavily to CO2 output. Farm animals release methane from their digestive systems, adding up to about 80 million tons per year or one-sixth of total methane emissions globally. Other activities include the clearing of large areas of forests for commercial and agricultural use of the land. The trees take in large amounts of CO2, helping keep concentrations down; removing vegetation contributes to global warming.

Reversing AGW

• Through conservation and other strategies, countries can reverse the trend toward increasing greenhouse gases. Reducing energy consumption, especially from fossil fuel sources, leads to lowered CO2 emissions. Sequestration, a technique that removes carbon dioxide and stores it in underground deposits, can also lower the concentration of greenhouse gas. Replacing coal- and gas-fired electric power plants with solar, wind and nuclear sources also reduces greenhouse gas emissions.